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Old 01-12-2013, 10:17 AM   #6
Dog Chauffeur
DRONE's Avatar
Joined: Oct 2007
Location: Tacoma, WA-ish
Oddometer: 4,024

OK, all this is kinda confusing for a dimwit like me. But . . .

The OEM rear moto wheel and tire for a 1150GSA is 150/70-17 with a diameter of about 25.5". Right now, I have a 155/80-15 Vredestein Snow+ car tire on the rear with a diameter of about 25". So I've lost about 1/4" in rear axle height because axle height depends on radius, not diameter. If I was to mount a 165/65-15 Vredestein Snowtrac 3 with a diameter of about 23.5" that would drop my rear axle height about 1".

That means then to balance out the front and rear, I'd need to drop the front axle by about 1" too. The OEM front tire is around 26". A 145/65-15 (like the Blizzak) according to that TacomaWorld calculator should run around 22.4" which sounds a little too short. With a 145/80-15 (Michelin, Firestone and Nankang make 'em) I get a diameter of about 24.2 which is just about right (.9" drop in axle height.)

But to complicate matters, I have a DMC trail reducer on the forks which is going to lower the front ride height, and a big spring (a 15-62) on my front Ohlins that heightens the front.

I'm thinking that maybe I should simply park the loaded rig on a flat piece of asphalt and get a buddy to take some pics from the side with me and Kirby on board. If it "looks" OK, then it's OK. If it "looks" too tall up front then it is, and if it "looks" too short, then it's too short.

I wonder how everybody else does this? Like when a builder is making custom leading-link forks for an outfit, how do they figure out how tall to make them?

After all this blather, I do have a question for DaveBig. I know that you've got the Dedone-style lower fork mount (so it doesn't change your ride height) and you have the OEM front shock with a 13-56 spring. With the Nankang 135/80-15 on the Stroker wheel, what is the height of your front axle from your garage floor? Is it, in fact, 11 3/4"?

BTW, here's another tire size calculator--
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