Bonneville America Forums Forums Technical Forums Custom Corner Bonneville Swingarm?

I was thinking that I read somewhere that the Bonneville swingarms are shorter than the Speedmaster and America. Is that true, or am I just wishing? I do remember reading that they were narrower, I think...

The widest tire you can fit in a Bonnie swing arm is a 170/180 with a rim change out, I believe I read somewhere. But Grzegorz is our local authority around here for definitive answers about Bonnies.

Tire width isn't a real big issue, rather wheelbase. I was thinking of using a Bonne swingarm to shorten up the wheelbase.

How much shorter do you desire to go? And what is the end result/benefit are you trying to achieve?

An inch or three, if that is what the Bonne was. Think bobber...

The tail end of our swing arms is a casting that plugs into the square tubes, couldn't you grind off the welds that hold the plugs, shorten the sq. tubes, plug the ends back in and weld it up? I would suggest you use the centerline of the swingarm pivot for pulling baseline measurements, if you want good results, your layouts for cuts and re assembly would have to be fairly precise.

That could work. I will have to look at my bike when I get home. I am trying to buy a spare frame to go with my spare engine. That frame does not come with a swingarm. So, before I order a swingarm, I figured I would ask around here first to see if the Bonne was already shorter. It may not be. Also, I may go hardtail instead. Not really sure yet.

If you go with a Bonny swingarm, run a narrow wheel , will the rear sprocket need to be shimmed out to match the front? I don't know, whenever you change something that's close but not engineered for, it always seems that small changes add up to surprise problems. Just saying from prior experience. I am sure of this, the centerlines of the front and rear wheels must match or the bike tracks wonky.

Good point. I planned on using a BA hub relaced to a wider and larger rim. So, maybe I should just swing for a SM/BA arm...

Bonnies run a 102 link chain, Spdys /Americas run 112 links, ergo they must be shorter.

According to my handbook for the 05 model year the wheel base for the Bonnie is 1493mm and for the Speedmaster it is 1655mm. When My wife gets home from swimming I will measure the swing arm on her Bonnie for you.

The BA/SM also has longer forks and more rake to add to the wheelbase. The more I think about it, I might be concerned with the thought of the Bonne having a narrower swingarm. And, that may simply be because of the shorter length. Don't tell anyone, but I may be using a 7" drag slick on this bike...

I just read the British Customs wide rear wheel description for the Bonneville. It states that the hub must be laced with an 1/8" offset to clear the chain. That is not good. So, I guess I will be using a stock BA/SM swingarm, or going hardtail...

you can compare both swing arms here and bonnies rear wheel spindle is smaller diameter

You are the man!!! Thank You!!

I read an article on a bike for the salt that was a thruxton frame with an America swing arm. done to increase stability at higher speed.

I think that is what I have floating in the back of my mind, but wasn't sure what the story was. So, it is probably Matt Capri's turbo bike...

to each their own, but I'd advise against it. when mine was slammed on 10 inch shocks I was basically sitting on the tire with the stock swing arm. and the tire would hit the rear cross bar and any fender I put on it with the stock tire and the 17 i'm running now.

but.. if you do - do it, post pictures and share!

I have a 200/60-16" on 12" shocks and the only interference I had, was where the Avon flared at the tread edge and the chain guard. Simple 1 minute fix with a side grinder.