collapse

www.dimecitycycles.com

www.cognitomoto.com

https://www.townmoto.com/collections/vanson-leathers

www.speedmotoco.com

www.CITYLIMITMOTO.com

www.jadusmotorcycleparts.com

www.lostapostlejewelry.com

www.sparckmoto.com

www.pistonsociety.com


Author Topic: "Doing it Right" or "How to Build a Functional Café Racer"  (Read 168113 times)

Offline AgentX

  • DTT BOTM WINNER
  • *
  • Posts: 963
Re: "Doing it Right" or "How to Build a Functional Café Racer"
« Reply #100 on: Jun 11, 2013, 00:40:22 »
Sonreir what about application streamlining? Going fast? What fairings have worked best for different sized bike historically, race application, etc?

To dovetail onto this, when does streamlining come into play, vs the additional weight of the fairings?  I am guessing the streamlining only matters at higher speeds.

For those of us riding at back-road speed on vintage machines, does a fairing really help us compared to the lighter weight of an unfaired bike, vs someone riding at track speeds?

Is a half-fairing or nose bowl a useful compromise in aerodynamics and weight, or just an ergonomic consideration for keeping wind blast off the rider?
"What's the use of having a motorcycle if you can't go tearing around staying out late?" Ralph asked reasonably.

Online Texasstar

  • DTT SUPPORTER
  • *
  • Posts: 5172
  • Can't is a four letter dirty word
    • Zoom With Zeke
Re: "Doing it Right" or "How to Build a Functional Café Racer"
« Reply #101 on: Jun 11, 2013, 01:07:18 »


You can see that the rider is fully encased by the fairing and the fairing comes to a point in the rear.  Though you can't see the front side, you can bet it's as circular as possible (including around the forks and front tire).  There's likely to be an air inlet for the engine, but that's about it.
[/quote]found a pic of the front
It's an optimization exercise and not a maximization trip.-Teazer


And though she be but little, she is fierce - WS
http://zoomwithzeke.com/
Third Times a Charm cb175
http://www.dotheton.com/forum/index.php?topic=66169.0

Honda Cb175 Victoria!

www.dotheton.com/forum/index.php?topic=52299.0

Honda Cb200 Lucky!
http://www.dotheton.com/forum/index.php?topic=45872.0

Bultaco El Montadero 360

http://www.dotheton.com/forum/index.php?topic=64349.0

Offline Sonreir

  • Moderator
  • DTT SUPPORTER
  • *
  • Posts: 11134
  • Oregon
Re: "Doing it Right" or "How to Build a Functional Café Racer"
« Reply #102 on: Jun 11, 2013, 01:42:37 »
To dovetail onto this, when does streamlining come into play, vs the additional weight of the fairings?  I am guessing the streamlining only matters at higher speeds.

For those of us riding at back-road speed on vintage machines, does a fairing really help us compared to the lighter weight of an unfaired bike, vs someone riding at track speeds?

Is a half-fairing or nose bowl a useful compromise in aerodynamics and weight, or just an ergonomic consideration for keeping wind blast off the rider?

Yup.  From a performance standpoint, a fairing is a benefit above a certain speed and a detriment below it.

About 40 years ago, a study was conducted by the US government to help determine the speed limits during the oil crisis.  They settled on 55mph because this was the average break-even point for most vehicles on the road at the time.

Though I haven't read much about the topic, I would expect motorcycles to do a little worse due to their poorer coefficient of drag.  Maybe 50mph or so?

Regardless, it's not uncommon to see fairings removed from bikes (especially the tiddlers) for tracks with only few straightaways.  Because motorcycles weigh so little in comparison to cars, any increase in weight represents a greater percentage change than our four-wheeled cousins would see.  Aerodynamics certainly matter for top-speed runs, but weight is still a serious consideration.  When overall performance is being evaluated.

Furthermore, you may find that a fairing reduces your drag enough such that top gear is no longer tall enough.  The most common way to attach this problem is to swap out the final drive to lengthen all the gears.  Well now you've gone and made acceleration worse as well as adding weight from the fairing.  It's definitely a balancing act.
Sparck Moto - http://www.sparckmoto.com

Audaces fortuna iuvat.

1977 Honda CJ360 - Café SOS - Stage One™, Café SOS - Stage Two™
1976 Puch Maxi - APuchalypse Now
Suzi T500 Cobra Resto

Custom Gauge Graphics
Custom Wiring Harnesses

DTT Red, White, and/or Black 360 Club - Better than those Blue guys

Online Texasstar

  • DTT SUPPORTER
  • *
  • Posts: 5172
  • Can't is a four letter dirty word
    • Zoom With Zeke
Re: "Doing it Right" or "How to Build a Functional Café Racer"
« Reply #103 on: Jun 11, 2013, 07:46:54 »
Sonreir I have been reading the posts of http://www.landracing.com/forum/index.php/topic,7612.0.html
And they said more time needs to be spent on developing the tail like Bret did on his bike.

However they like other forums have criticized Bret's design because it is sucking him off the bike...so he duct taped his hump on his leathers and fixed the problem. (Love this guy)
"Most of us that have raced LSR bikes have know for some time that the "back end" is what it is all about
When we used the windtunnel back in the early 1970's for the 125c.c. Can-Am effort we saw what a
special long tail did for Aero.  What we did not know at that time was how to get the chassis to work
with the long tail........Brett and Joe got the bikes to handle....they have solved this problem.  Also until resently the rules did not allow for a "long back end"....Thankfully the "officials" have seen the error in their "old rules" and the sky is now the limit for a sit-bike"
The complete string is worth a read...I have attached a pic of Joe Amo's bike.


It's an optimization exercise and not a maximization trip.-Teazer


And though she be but little, she is fierce - WS
http://zoomwithzeke.com/
Third Times a Charm cb175
http://www.dotheton.com/forum/index.php?topic=66169.0

Honda Cb175 Victoria!

www.dotheton.com/forum/index.php?topic=52299.0

Honda Cb200 Lucky!
http://www.dotheton.com/forum/index.php?topic=45872.0

Bultaco El Montadero 360

http://www.dotheton.com/forum/index.php?topic=64349.0

Online Texasstar

  • DTT SUPPORTER
  • *
  • Posts: 5172
  • Can't is a four letter dirty word
    • Zoom With Zeke
Re: "Doing it Right" or "How to Build a Functional Café Racer"
« Reply #104 on: Jun 17, 2013, 13:13:45 »
Sonreir, I have been reading Phil Irving's book "Tuning for speed" and since e85 was not available at that time I was wondering if you could address how to tune a street motorcycle for increased performance with e85.  There seems to be a dispute about the octane rating of e85.  In Texas they say it is 114 but Wiki says 95.  So if we decide to increase our compression to 12:1 are there any other things we need to do to take advantage of e85?  I guess what I'm trying to say is can you address tuning for different fuels for speed?
It's an optimization exercise and not a maximization trip.-Teazer


And though she be but little, she is fierce - WS
http://zoomwithzeke.com/
Third Times a Charm cb175
http://www.dotheton.com/forum/index.php?topic=66169.0

Honda Cb175 Victoria!

www.dotheton.com/forum/index.php?topic=52299.0

Honda Cb200 Lucky!
http://www.dotheton.com/forum/index.php?topic=45872.0

Bultaco El Montadero 360

http://www.dotheton.com/forum/index.php?topic=64349.0

Offline Worst cb650 ever

  • Posts: 1491
  • You can always get it running with time or money.
Re: "Doing it Right" or "How to Build a Functional Café Racer"
« Reply #105 on: Jun 17, 2013, 13:28:58 »
I can't speak to the octane, but I do know that e85 has about 30% less power per gallon, so you generally need to flow about 30% more fuel to make the same power as regular gas. 

On forced induction (turbo / supercharged) vehicles, the e85's high octane and cylinder cooling effect allow running higher boost on an otherwise stock vehicle, but larger fuel injectors and a higher capacity fuel pump will still be required. 

I wonder if just running 93 octane pump gas would give you what you are looking for without having to deal with the detriments of e85?
DTT Blue (cause Winter is Coming) CB360 Club.

1995 CBR900RR - a winter flip not worth a DTT writeup - Sold

1986 Yamaha SRX600 - mailed to me from California - build coming soon?

1983 VF750F

1976 CB360T

1993 CBR900RR - Sold

1979 CB650 - Sold

Offline Nebr_Rex

  • DTT SUPPORTER
  • *
  • Posts: 879
Re: "Doing it Right" or "How to Build a Functional Café Racer"
« Reply #106 on: Jun 18, 2013, 01:22:49 »
 Gas - 14.7/1 ,high btu
 E85. - 9.7/1   ,lower btu
 With the extra fuel being used it's about a 10% increase with the correct air fuel ratios.
As for octain rating I've heard 104.

Offline Worst cb650 ever

  • Posts: 1491
  • You can always get it running with time or money.
Re: "Doing it Right" or "How to Build a Functional Café Racer"
« Reply #107 on: Jun 18, 2013, 10:05:56 »
Good to know, thanks!
DTT Blue (cause Winter is Coming) CB360 Club.

1995 CBR900RR - a winter flip not worth a DTT writeup - Sold

1986 Yamaha SRX600 - mailed to me from California - build coming soon?

1983 VF750F

1976 CB360T

1993 CBR900RR - Sold

1979 CB650 - Sold

Offline gas_fiend

  • Posts: 20
Re: "Doing it Right" or "How to Build a Functional Café Racer"
« Reply #108 on: Jun 21, 2013, 02:12:30 »
this is a great thread! makes me want to build an engine so badly

Offline alex2445

  • Posts: 114
Re: "Doing it Right" or "How to Build a Functional Café Racer"
« Reply #109 on: Jul 14, 2013, 05:28:31 »
Thanks Sonreir I'm gonna keep this forum in my favorites or something, that way when I wanna rebuild an engine a lot hotter, I can look at this and do it  ;D
There's always tomorrow