Rims and Tires for a Narrow Case

[blaat!]

Getting ready to re-lace my wheels with new rims. I'm looking for suggestions on what size rims and tires would provide optimum handling for the road on a narrow case chassis. I'm not going for OEM fidelity, but rather overall ridability and handling.

I understand that both rims should be 18 inch diameter, but how wide? Front? Back?

What about the tire sizes? Front? Back?

Thanks.
-Jim

[blaat!]

Seems like WM2 (1.85) x 18" for both front and rear would be a safe bet for the rims, no?

[double diamond]

Jim,
As I recall, you're working on something along the lines of a Mach 1 replica. I'd suggest one WM size smaller on the front than the rear. So WM1 front/WM2 rear. Race builds seem to favor WM2 front/WM3 rear but you don't need to go that wide on a street ride. Tires would be 2.50x18 front, and a 2.75 or 3.00x18 rear. Matt

[blaat!]

Thanks Matt, that is helpful.

I'm planning to put together a completely custom bike using the frame and bits I have. Since it has been determined that the chassis I have is not from a Mach 1, I will not feel bad cutting it up, modifying, and customizing.

I'm currently rebuilding the engine I have to original Mach 1 specs. Simultaneously I'm going to keep my eyes open for a replica or something that can more easily be converted to a Mach 1 and hopefully put the engine in that.

If everyting works out (and I live long enough), I'll put the Mach 1 engine in the replica (making it sorta legit?) and use the other engine for the customized bike.

Whew, that said, I may opt for the WM2 front and WM3 rear so I can get wider tires on it... I don't really want to put wider tires on just to make it look sporty if they provide no improvement over narrower tires though

-Jim

[flynbulldog]

from what I understand lighter is always better when the limit of adhesion is not a factor.

A lot of the racers in the CB160 class have switched to WM1 both front and rear and they are using the Bridgestone racing tire that came standard on the Honda dream 50 racer
Many of the riders are reporting 1.5 to 2.5 seconds per lap improvement with these new lighter set-ups.


I got a set of wm1s that were on a 250 racer back in the 80's and I'm considering putting them on my 250 race bike.
The tires are Bridgestone BT39SS:

They make a street version for 17 inch wheels but the race version is made for WM1 18s

[blaat!]

So...

Wide (wheels and) tires are heavier making it difficult for the suspension to put the tire back in contact with a rough road, and may provide excessive contact area when the road is smooth. This situation seems like it would give inconsistent grip to the road - sometimes too much and sometimes not enough... and additional unsprung mass.

Thin tires are lighter allowing the suspension to return the tire quicker on a rough road, have less unsprung mass, but have less contact area when the road is smooth.

Sounds like it is a matter of finding the sweet spot between tire contact area and wheel weight?

Since the HP and weight are relatively small, it probably makes sense to go with thinner wheels/tires?

[flynbulldog]

Blatt,

I think things like total bike and rider weight, cornering speed, and type of use all come into play. If you're racing the bike you may be able to over ride the tires capabilities and therefore wider rubber would be the call. In that case you may need to sacrifice a little weight and therefore a little nimbleness in order to get the amount of tire needed.
You can always adjust suspension damping to overcome more unsprung weight, don't try to match the wheel weight to the suspension, match the suspension to the bikes overall needs

But if you plan to ride on the street, in normal conditions (dry) you'll likely never over ride the tires so why not make it as light as you can?

I'm not saying the little tires from the dream are the answer but I do think I'd try to stay as light as possible.

I'm struggling with this same problem right now with my 250 racer. I have a good pair of wm1's but I'm planning to use a big heavy 4 leading shoe drum up front so in the end I'll probably opt for a wm2 front and a wm3 rear. I don't believe it's the best choice for all out racing but its just how I want to equip the bike. I've made several choices on this bike that are not the best for racing but to me they make a better over-all bike

I guess I'm contradicting myself but there you have it. good luck with your choice.

And yes, I think your logic is sound.

[flynbulldog]

So...

Wide (wheels and) tires are heavier making it difficult for the suspension to put the tire back in contact with a rough road, and may provide excessive contact area when the road is smooth. This situation seems like it would give inconsistent grip to the road - sometimes too much and sometimes not enough... and additional unsprung mass.

Thin tires are lighter allowing the suspension to return the tire quicker on a rough road, have less unsprung mass, but have less contact area when the road is smooth.

Sounds like it is a matter of finding the sweet spot between tire contact area and wheel weight?

Since the HP and weight are relatively small, it probably makes sense to go with thinner wheels/tires?

In addition to the reasons you post here less wheel/tire weight also affects the bike's ability to change directions or "flick" from side to side.
Wheel/tire weight has a major effect on how nimble or sluggish the bike feels when turning (pushing into a lean).
As mass increases gyroscopic force of the spinning wheels is increased making changing direction require more effort.

This video demonstrates how much force is created when a wheel is spinning and increasing mass increases force.

http://www.youtube.com/watch?v=8H98BgRzpOM&feature=related

I'm not saying that it's critical for a light nimble 250 to have the lightest wheels you can find because no matter what you use a 250 Ducati is going to feel light and nimble.
But lighter wheels will give you a noticeably lighter feeling (require less effort) in turning and changing directions.

[blaat!]

Can anybody think of OEM alloy rim brands that were produced before the 1980s other than the list below?

Akront
DID
Takasago
Borrani

Also, does anybody know of specific bike models that had alloy rims that would be interchangable with a Ducati single? I know some of the 60s-80s MX/Scramblers had alumiunum rims (OEM or aftermarket) with 36 spoke drum brake hubs. I would be particularly interested in models that were higher volume mass produced in the US as they would be easier to acquire, but any shared knowledge would be appreciated.

Trying to find a decent set of rims to re-lace onto my hubs without killing the restoration budget.

Thanks!
-Jim

[blaat!]

Just got my new shouldered alloy rims, WM2 front and WM3 rear. Ordered my spokes. I'll be removing and polishing the hubs over the next few weeks, then lacing them up.

I've been researching tires a bit and I'm thinking of getting Avon RoadRider tires.

Front: 90/90-18 51V
Rear: 100/90-18

Anybody have experience with these or Avon in general? Any other tires you would recommend more? How about Bridgestone Spitfire? I don't plan to race the bike, so I'll need tires for the streets.

Thanks.
Jim