New Guy. Lots of Motorcycle Related Questions.

[Vintage_Honda_Garage]

Hello. I mentor a high school after-school bike building program and this year we are shooting for the salt with a M-BG Honda CB350. I have a few questions as this will be our first time doing something like this.

First question: Would a cafe style "bump seat" be considered partial streamlining? Something like this?

[TheBaron]

Nope, you are good ,,,,,, You should get a SCTA rulebook as it is pretty much the bible across all land speed venues..

Robert in California

[Vintage_Honda_Garage]

Nope, you are good ,,,,,, You should get a SCTA rulebook as it is pretty much the bible across all land speed venues..

Robert in California

I have the 2019 book. I just was uncertain if this bump would be considered streamlining or not.

[Vintage_Honda_Garage]

Next question for the bike guys, looking for tire recommendations. Stock size for this model is 18-100/90 in the front and 18-110/90 in the rear.

[wobblywalrus]

These old 350's are raced in the UK on tracks and road circuits.  Get a copy of "Classic Racer" magazine from the UK.  There are ads in it for race tires in the narrower old widths and lots of other useful items.

[Doc B.]

I think those sizes may be quite a bit larger than stock tires for the CB350. If I have the stock rim widths right (1.6" front a.k.a WM0, 1.85" rear a.k.a. WM1) they were set up at the factory with narrower tires like 3.00-18 or 80/90-18 front and 3.50-18 or 90/90-18 rear. Even those tire sizes seem a bit wide for the rim sizes - back in the 70s Honda seemed to fit wider tires on a rim than the tire manufacturers recommend these days. On a smaller displacement bike on the salt you might get a small advantage in rolling resistance with a skinnier tire. I think you could even go down to a 2.75-18 front and a 3.00-18 rear on the stock rims. If you're flush, Avon has race tires in the proper sizes. Don't know how much advantage they would have beyond a higher speed rating than some street tires in those sizes. Avon Streetrunners are S rated - 112mph and reasonably priced. I run S rated Heidenaus on my nitrous CB77. Record in the fastest class I run in is 108, so they are good for now. I run a very skinny front, 2.50-18 K40, on a kind of oddball 1.4" skinny wheel. Rear is a 3.00-18 K33 on an XL350 aluminum rim that is, IIRC, 2.15" a.k.a. WM2.

[Vintage_Honda_Garage]

I think those sizes may be quite a bit larger than stock tires for the CB350. If I have the stock rim widths right (1.6" front a.k.a WM0, 1.85" rear a.k.a. WM1) they were set up at the factory with narrower tires like 3.00-18 or 80/90-18 front and 3.50-18 or 90/90-18 rear. Even those tire sizes seem a bit wide for the rim sizes - back in the 70s Honda seemed to fit wider tires on a rim than the tire manufacturers recommend these days. On a smaller displacement bike on the salt you might get a small advantage in rolling resistance with a skinnier tire. I think you could even go down to a 2.75-18 front and a 3.00-18 rear on the stock rims. If you're flush, Avon has race tires in the proper sizes. Don't know how much advantage they would have beyond a higher speed rating than some street tires in those sizes. Avon Streetrunners are S rated - 112mph and reasonably priced. I run S rated Heidenaus on my nitrous CB77. Record in the fastest class I run in is 108, so they are good for now. I run a very skinny front, 2.50-18 K40, on a kind of oddball 1.4" skinny wheel. Rear is a 3.00-18 K33 on an XL350 aluminum rim that is, IIRC, 2.15" a.k.a. WM2.

All good info. Thank you. Our goal is 121 mph so we'll need a higher rated tire.

[Vintage_Honda_Garage]

Next question: Suspension.

What kind of setup do we want in the front and back? Stiff? Soft? Normal?

[donpearsall]

Whatever suspension you choose, make sure that the bike and rider are as low as possible. Less wind resistance.

In your class, the stiffness of the suspension will not matter much. For high power, fast bikes that are prone to rear wheel slippage keeping the wheels on the ground is the most important thing so a fast rebound is best.

So in your case, the stock suspension will be fine, just make sure you set the height as low as physically possible and within the rules.
Good luck,
Don

[Vintage_Honda_Garage]

Whatever suspension you choose, make sure that the bike and rider are as low as possible. Less wind resistance.

In your class, the stiffness of the suspension will not matter much. For high power, fast bikes that are prone to rear wheel slippage keeping the wheels on the ground is the most important thing so a fast rebound is best.

So in your case, the stock suspension will be fine, just make sure you set the height as low as physically possible and within the rules.
Good luck,
Don

Awesome. Thanks for the insight.

[Koncretekid]

Great project bike with all kinds of speed parts available.  I'm writing a book on "How to Make a Slow Bike Fast", so I'm very interested in your project.

Where are you located and where/when do you expect to have it finished?

Here is a photo of my M class  250 record holding bike.



Tom

[Doc B.]

Our goal is 121 mph so we'll need a higher rated tire.

Mickey Thompson makes a 2.50/2.75-18 drag front tire.

Avon Roadriders come in various street and race (AM-26) types, in sizes that might work.

If I ever get to the point of needing a higher speed rating I might look at that Thompson front and an Avon Roadrider 110/80 V 18 rear, which is rated for 2.15-3.0 rims.

My experience is limited to one year on very smooth hard salt and one year on rutted salt with soft spots where even my peewee nitrous 305 was spinning a little here and there. I was glad to have a fairly stock suspension with some travel on the rough stuff.

I'll suggest putting some energy into figuring out how to reduce your own frontal area as much as possible along with lowering the bike. Try to wrap yourself as tight as possible onto the bike. Get snug leathers that won't flap in the breeze. My bud Jaylin Billig says she "looks like a bug hanging on for dear life" on her CB175.

@Koncretekid - lovely bike!

[Vintage_Honda_Garage]

Great project bike with all kinds of speed parts available.  I'm writing a book on "How to Make a Slow Bike Fast", so I'm very interested in your project.

Where are you located and where/when do you expect to have it finished?

Here is a photo of my M class  250 record holding bike.



Tom

We are based out of Milwaukee, WI and hope to be at Speed Week 2021

[Vintage_Honda_Garage]

Our goal is 121 mph so we'll need a higher rated tire.

Mickey Thompson makes a 2.50/2.75-18 drag front tire.

Avon Roadriders come in various street and race (AM-26) types, in sizes that might work.

If I ever get to the point of needing a higher speed rating I might look at that Thompson front and an Avon Roadrider 110/80 V 18 rear, which is rated for 2.15-3.0 rims.

My experience is limited to one year on very smooth hard salt and one year on rutted salt with soft spots where even my peewee nitrous 305 was spinning a little here and there. I was glad to have a fairly stock suspension with some travel on the rough stuff.

I'll suggest putting some energy into figuring out how to reduce your own frontal area as much as possible along with lowering the bike. Try to wrap yourself as tight as possible onto the bike. Get snug leathers that won't flap in the breeze. My bud Jaylin Billig says she "looks like a bug hanging on for dear life" on her CB175.

@Koncretekid - lovely bike!

We ended up going with the AM-26 Avon Roadriders. 90/90 in the front and 110/90 in the back (smallest we could get). We also spent up a bit and got Nachi bearings along with aluminum rims.

[Vintage_Honda_Garage]

Another seat question.

Rule 7.F.4.b states "Rear fenders shall extend rearward to a point not less than a vertical line drawn through the rear axle. A seat that covers the rear wheel to the vertical line may substitute for the fender requirements."

This is the seat we are probably going to go with since we already have it (aka its free). This appears to fall within the aforementioned rule, correct? Also, this would not be considered streamlining correct?