how solid is this rotor adapter setup

I found this in a CX500 build thread, and i think it's about the only option for the rims I have. Comstars, with through holes on the hub. Original used two rotors and 110mm bolts, but the bolts had nuts from the other side.

This design would have the bolts threading directly into the aluminum, plus the bolts would be longer by whatever the adaptor thickness is.

Would this still be a viable solution for me? Any reason this would be less safe to run?



 

doc_rot

Oh the usual... I bowl, I drive around...
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I don't see any problem with that. those bolts are mostly subjected to shear forces so they don't need to be torqued very much. Seems like that assembly is adding unnecessary weight though. Are these a product you can purchase? Or would you have to make /source your own. I bet you could come up with a lighter solution, perhaps adding a threaded insert into the existing holes so you dont have to through bolt.
 

teazer

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I agree with Doc-rot. check your existing rotors for pitch center for the holes and diameter of the center and see if EBC lists a disk rotor with the same/less/more dish but the same center.

You can often find a similar rotor for a different bike that will work with your set up of forks, hub and calipers. Modern hubs are usually wider than our old bikes that came with skinny forks, so think about what you are trying to fit together and see if there's something available that might work.
 
I've come across A LOT of threads and never see a anyone mention anything but:
1. Adaptors/spacers for rotors
2. Running the stock sport bike 17" front wheel
3. Custom rotors.

I have to get calipers before I figure my exact measurements, but I doubt I'd find a rotor that matches not only offset but diameter and bolt pattern.

A member on here did go with custom rotors, which is the nicest solution, but they are a little out of my budget for now.
 

teazer

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Probably right, but it's worth checking to see what's out there before embarking on a more expensive path.

Which rotors are you using - stock or something sexy and newer and lighter?
 
Probably right, but it's worth checking to see what's out there before embarking on a more expensive path.

Which rotors are you using - stock or something sexy and newer and lighter?
yes, that's why i'm still in the "design" phase.
The forks are '99 GSXR750. The rotors too.

The rotors were an eBay fail. They are at minimum thickness, and someone had attempted to turn semi-floating into full floating rotors but i guess it proved too much work so they just got 3 of the 5 bobbins done on one of the rotors. The things dumba$$ kids do, because some guy on the internet posted this "cool new mod" is ridiculous.

So it likely won't take much for me to ditch these rotors. If it drags out long enough, maybe i'll just convince myself to get new custom ones. Would probably be around $600-650 CAD for me i think. But, they'd be new *shrug*

Getting the GSXR front wheel is the easiest solution and seems the one most guys go after, but i just don't like the look of the small 17" front wheel. I like the 17 rear 19 front look. (Yes, that has its own challenges (like header clearance) but hoping we'll be fine. Others have done the same)
 
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teazer

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I think SRAD fork are 214mm between centers and they use 5 hole 320mm disks with 4 pot calipers. Hubs are 130mm across (side to side) and disk rotors are pretty flat (zero offset) so they would have to be spaced out a long way from the hub to avoid calipers and spokes intersecting if you use a narrow hub and spoke up a new rim. On Comstars I have no idea how much clearance you will need. Time to start taking a lot of measurements.

750 SRAD disks were 5mm stock and 600 were thinner at 4.5, so your rotors might work as long as you get a set bobbins to make them fully floating. The centers will wear much faster with floaters, but I don't expect that you will be doing lots of fast miles on the bike.

The other alternative is to get a wide CognitoMoto front hub which I thing is designed for a spoked wheel with GSXR forks and brakes.

Or, as you said, use the GSXR forks and brakes with that Comstar front wheel and get custom rotors made or buy that conversion kit - if it fits.

That's why most guys go full matching GSXR front end, wheel and all. The bits work well together and it's cheaper in the long run.
 
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The comstar is 80mm, so 50/2=25mm or 1 inch per side. That is not bad, considering its 6061 aluminum for the adapters.

For this reason I went with older GSXR forks instead, because they are not radial mount calipers. Therefore if necessary, I can space the calipers in/out a little bit to get everything to line up right, so it's definitely a bit more flexible.

I need to get calipers before I can really get serious about measurements, but I'm having a hard time deciding which calipers to go with. I'm still trying to find dimensions on the gsxr calipers so I can see how far they stick out on the inside to see how much room there would be (if any) against the comstar spokes.

Also, I have two sets of tubes. 1999 750 and 2001 1000, the mounts are different but I dont know if the calipers are. Part of me thinks maybe just adapting original 1983 honda calipers on here wouldnt be a bad idea because they are the sliding type (with pistons on one side only) so I know they would clear for sure.

Here is the bike as it sits with the front fork and 19" wheel. I'm using the stock 25mm gsxr axle with 42x25x9mm bearings and custom machined spacers

Below is the comparison between the 1999 and 2001 forks. You can see the difference in mounting brackets between the two. The '99 is on the left.

Interestingly, the 2001 forks are slightly shorter. Not by much, but I need all the height I can get so it will likely be the '99 tubes.


20200329_214015.jpg
20200307_142152.jpg
 
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ex119x

Member
The Honda brackets for the sliding calipers probably use different spacing than the suzuki forks. Look at the calipers from an SV650. They are also dual piston sliding type caliper and I think the mounting spacing is compatible some of the GSXR forks. They are available pretty cheep on ebay.
 
The Honda brackets for the sliding calipers probably use different spacing than the suzuki forks. Look at the calipers from an SV650. They are also dual piston sliding type caliper and I think the mounting spacing is compatible some of the GSXR forks. They are available pretty cheep on ebay.
Yes, I'd have to make an adapter to fit the calipers onto the forks. More work but maybe not a bad thing because it could help make the hub spacers that much thinner and lighter. I have lots of 1/4" and 3/8" aluminum plate around here.

I will certainly look into SV650 calipers. Very well possible they might fit. That would be ideal. Might have to join a SV650 group for this. Thanks!
 

teazer

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SV calipers are similar mounting bolt spacing as the 2001 forks/caliper, but not the same. I would just use the 1999 calipers with the matching forks.

In my stash I found two pairs that appear to fit 1999 but very different thickness overall and different piston diameters and I have no idea what the second pair came from.
 

teazer

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So here's what I found.

Bottom right: 1991 GSXR Nissin caliper, 91mm bolt spacing, 34/30 pistons x 2
Top right: 99 GSXR ??? Tokico, 91mm bolt spacing, 30/27mm pistons x2
Top left corner: 2001 GSXR 62mm bolt spacing, 30/27mm pistons x2
Bottom Left: SV650 sliding caliper, 55 mm bolt space, 30/30 x1 pistons

Interesting that the Top right will fit a set of 99 forks but has the same piston pairs and the later 2001 caliper.

I cannot tell you what master cylinder bore went with those, but I found a couple of charts on line that suggests that all TL1000 had 320mm disks and 91mm bolt spacing. TL1000S were 4 pistons and TL1000R were 6 piston. I was led to believe that the Nissin small piston 91mm space calipers were from a TL1000. Forks supposedly also but the lower triple said 99 GSXR. SRAD and TL1000 were 214mm fork centers.

SRAD (99) GSXR also had 320mm rotors and 91mm bolt space.

2001 (k1) came with 320mm rotors, 4 piston calipers and 207mm fork centers.

I can confirm that my 99 SRAD or TL1000 forks are 214 and my K1 (2001) are 207mm fork centers.

You can create your own spreadsheet to calculate the force at the bars with different piston diameters and caliper bores. Your bike should be lighter than an SRAD so the same force at the lever may well genearet excessive braking force. Kevin Cameron included his calcul;ations which are more sophisticated than the Michael (Mercury) Morse table on Vintage Brakes web site. It allows for teh effect of disck roto diameter and bike and rider mass.
 

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So here's what I found.

Bottom right: 1991 GSXR Nissin caliper, 91mm bolt spacing, 34/30 pistons x 2
Top right: 99 GSXR ??? Tokico, 91mm bolt spacing, 30/27mm pistons x2
Top left corner: 2001 GSXR 62mm bolt spacing, 30/27mm pistons x2
Bottom Left: SV650 sliding caliper, 55 mm bolt space, 30/30 x1 pistons

Interesting that the Top right will fit a set of 99 forks but has the same piston pairs and the later 2001 caliper.

I cannot tell you what master cylinder bore went with those, but I found a couple of charts on line that suggests that all TL1000 had 320mm disks and 91mm bolt spacing. TL1000S were 4 pistons and TL1000R were 6 piston. I was led to believe that the Nissin small piston 91mm space calipers were from a TL1000. Forks supposedly also but the lower triple said 99 GSXR. SRAD and TL1000 were 214mm fork centers.

SRAD (99) GSXR also had 320mm rotors and 91mm bolt space.

2001 (k1) came with 320mm rotors, 4 piston calipers and 207mm fork centers.

I can confirm that my 99 SRAD or TL1000 forks are 214 and my K1 (2001) are 207mm fork centers.

You can create your own spreadsheet to calculate the force at the bars with different piston diameters and caliper bores. Your bike should be lighter than an SRAD so the same force at the lever may well genearet excessive braking force. Kevin Cameron included his calcul;ations which are more sophisticated than the Michael (Mercury) Morse table on Vintage Brakes web site. It allows for teh effect of disck roto diameter and bike and rider mass.
Hey, great post!

Can you do me a favor and measure the width, especially from the pad toward the rim .... to know how much they would stick "in", for top left and top right.

While I agree those 62/91mm measurements will work with the 01/99 forks, I could have sworn the 99 SRAD came with 6 piston calipers, not 4?!

Honestly, I'd prefer the 4. Less to rebuild and aparently the 6 were never that good anyways.

If the width works, I'd rather just go with stock bolt on ones instead of making adapters for the calipers.

The rotors I have are 5 bolt, 320mm and I think 54mm bore hole, as shown on the chart for 99 SRAD.

THANKS FOR THE HELP!!!!
 

teazer

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From the center line of the caliper - which is the center of the disk, all three double sided are 41-42mm to the inner side where they are closest to the spokes. TL100R I think was the one with 6 pot calipers, but no need for that complexity and the longer 6 piston caliper is more likely to flex than shorter 4 pot calipers.
 
From the center line of the caliper - which is the center of the disk, all three double sided are 41-42mm to the inner side where they are closest to the spokes. TL100R I think was the one with 6 pot calipers, but no need for that complexity and the longer 6 piston caliper is more likely to flex than shorter 4 pot calipers.
Ok, that seems less than I expected, which is good.

Wheres the mounting point in relation to that centerline? Aka, how far in from the mounting point can I expect the rotor centerline to be with those calipers? I'm sure the mounting point isnt a full 42mm the OTHER way.

I just measured and I have about 66mm on the lower mounting bolt from the mounting point to the spokes and about 80mm on the upper bolt. 66mm sounds a little on the low side if that mounting point is too dar off the caliper centerline.

If I could get that measurement I'd be much obliged. No rush. Whenever you get a chance!
 

teazer

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26mm from the inside of the fork leg/outside of the caliper to the center line of the disk rotor.

+/- about 1mm.

You might get away with shaving a small amount off the lower inside face of the caliper, but I think I see a GSXR front wheel in your future.

What rear wheel are you using?
 
26mm from the inside of the fork leg/outside of the caliper to the center line of the disk rotor.

+/- about 1mm.

You might get away with shaving a small amount off the lower inside face of the caliper, but I think I see a GSXR front wheel in your future.

What rear wheel are you using?
I'm not going 17" front under no circumstances. This guy did it using radial brakes, which should be even tougher to pull off. I dont know how much he had to shave off the inside, but its clear hes using spacers to bring the caliper as far back as possible. I'm pretty sure it's the exact same comstar wheel.

My rear wheel is a 17" from a '92 nighthawk. Using the original '83 20mm axle instead of the 92's 17mm. The rear spacers are finished and I'm happy with the way it sits with a 150/70/17 tire.

Thanks for the numbers! It should help me figure out the caliper situation. I might PM you for the exact model of them if I decide to go with those 4 piston ones. I agree, the 6 piston ones are probably not my best option.
 

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@teazer .... So, i took a gamble on the '99 GSXR calipers and lost ... kind of. Found a set being sold from within Canada, so couldnt pass them up.
The inside of the calipers ended up being thicker than i anticipated, and they don't clear the spokes. Again, a note to anyone doing this .... this is why people stay away from the "reverse comstar" wheels and go for the earlier comstars! They stick in more than can be ground off.

Now, my options are:
1. Bracket for current calipers - bolt a bracket to the OUTSIDE of fork. Bolt the caliper to the INSIDE of the bracket using 5mm spacers to bring the caliper in just enough, but not as far as stock location. Similar to pic below where they are using a bracket to adapt GSXR calipers to an SV650.
2. Different calipers - which won't match the 91mm bolt spacing and will need an adapter anyways ... plus the cost of yet another set of calipers.
3. Just get a GSXR wheel - Don't want to admit defeat and go this route just yet.



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teazer

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Key dimensions/parameters are where is the disk rotor relative to the spokes. That's where you have to start because the caliper has to be centered on the disk, so play with that first. Then see what the caliper to fork adapter has to look like.

If the rotor has to move out so far that it touches the fork slider, then that combo of triple trees, wheel and caliper will not work. With GSXR forks and triples that is unlikely to be a constraint in this case. Use washers to simulate the rotor spacers.
 

Rider52

Active Member
Caliper size is a major problem with Harley to sport bike brake conversions. Can you shave a bit off the back side of the calipers? That is the common practice on the HD conversions. The solution I used on my Evo chopper was asking the EBay sellers to measure the calipers width. EBay is full of Tokico and Nissan calipers and it didn't take long to find one that worked for my application.
 

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