How I'm increasing tire size on my MS for more HP and performance

[Mechaniac]

Most here probably know I'm working with Racing Ray to improve the power level of the engine and I shaved some weight off of the flywheel with good results, tuned in the fuel curve with the existing tuner. While discussing the project with Ray he often offers up his expert opinion on what else I should do for the best results. So, I listen to him closely, ask questions, and take notes.

One of the subjects he brought up was gearing change. Usually when he completes an engine power increase, he recommends steeper gearing to take advantage of the increased power. Picture this, a bike is geared pretty close to optimal as delivered. If you run the quarter mile as quickly as possible you should be at the end of the power band in the appropriate gear. When you increase the power and can maintain traction to match the previous launch you will likely achieve the same speed in a shorter distance and be out of RPM unless you throw in another shift that really doesn't accomplish anything because you are already going so fast and near the end of the track it's effect is negligible. To get some of the RPM used to accelerate faster in the same distance you must decrease the gearing leverage, or lower the gearing ratio. If you are racing a motorcycle with rear chain drive and you can swap sprockets you're good to go, almost any ratio in reason is easy to install. But on shaft drive bikes like ours one is limited to what is available. Honda made two ratios, ASAIK Kawasaki only made one. So what is one to do? There are two ways, transmission gearing and rear tire diameter.

The Mean Streak comes with a nice close ratio gear box so short of custom made gears all slightly taller the better solution is a taller rear tire. All gears now have a wider range. With more power one can still wring out the quarter mile in the 4th gear but get there quicker and at a higher speed. He recommended a larger diameter rear tire for this project. Now 5th gear is fun and that where the telephone poles start to look like a picket fence but for the timed quarter mile it is irrelevant. Since this is realistically a muscle cruiser that's more at home on the Boulevard than the road racetrack, I chose to change out just 5th gear as well. One just needs to obtain the steeper still Vulcan Classic 5th gears. This does require a case separation, whereas the tire while still good does not. This ratio will allow a deep overdrive for lower RPM highway flying and better fuel efficiency just coming and going. Maximum top speed in the quickest time for the crotch rockets, relaxed efficiency when the drag race is over for me. Combining the tire and 5th gear is the best availible option though also more costly due to gear installation.

I know all about chassis dynamics and that just changing the rear tire like most do would change other things that I didn't want to upset in a negative performance direction. So, I pulled out the books, calculator, and started researching prior posts. This is what I came up with and why. Some one just asked about it on another Vulcan form and I wrote this answer, now I'm sharing here where I feel more at home for this bike.

On my 2008 Mean Streak I'm in the process of going a half inch bigger front and rear. Same width up front as OEM but 20 mm wider in rear. I come from a long background in successful chassis modification in automotive and motorcycle, not the best but pretty solid. It all depends on what you're trying to achieve.

First off, my OEM speedo which goes off the REAR wheel on the bike is already about 3% faster than actual, this will make that more accurate. Let's get that out of the way.

If you add a larger rear tire to increase traction from a dig or just for looks but do not change the front suspension on a motorcycle, you will reduce front axle trail and rear axle anti-squat. Yes, the front end feels more turn able because it has less centering force. But the angle is shallower and darty, less predictable, I've seen others on the forums describe this as "sporty". Anti-squat is decreased slightly if you don't adjust the front. This should slightly increase trail while increasing the center of gravity's distance from the contact point of the tires. Should be better to turn. I checked, there's still a little room in the fender.

The increase I'm putting in profile on the front could increase flex between contact patch and wheel, to counteract this I'm going to Bias-Ply in the front due to the stiffer side walls than radials. Two OEM's are doing this exact thing on similar bikes, like the HD Breakout.

This bike, a 2008 MS, sits really low, a half inch higher will not be dumb looking. It will increase the cornering angle limit which I hit at times, scraping the bottom of my boot on a corner is always un-nerving. I may need a longer Vulcan kick stand, don't know until I get them on.

Diameter has a larger effect on traction start and stop than width. Ask any experienced drag racer they would rather use a taller tire than wider when able as long as gearing is appropriate for the change.

With the increases in power I've done and have planned this bike is already laying rubber shifting into 3rd gear and pinning the throttle, besides the increase in traction start/stop the reduction in gear leverage but increase in speed will be the expected result.

Stopping power on this bike is traction limited with the big MS brakes, so stopping distance should drop.

The tires I accomplished this with are Avon Cobra Chrome. Hard to find the correct sizes and construction, and intended use design, load ratings, etc. This was the way.

I have the tires, getting rare and pricey. I'm too busy with other stuff to put them on and report back unto next month at the soonest.

I recommend these books to explore motorcycle suspension design and tuning:
Race Tech Motorcycle Suspension Bible, and
Total Control by Lee Parks

Vernon

[Mechaniac]

BTW, I just realized I could look up the sizes I came up with by looking at my email. I was going to post it when I got home and looked at notes and the tires. They are:

Avon Tyres Cobra Chrome Rear Tire (190/60R-17)

Avon Tire Cobra Chrome Front Tire (130/80B-17)

I actually got them off of Amazon for about $450 from separate vendors.

Vernon

[andyvh1959]

Increasing the diameter of the rear tire will have no negative impact on the chassis geometry. The Vulcan chassis geometry for the Classic, Nomad and Mean Streak is very conservative, lots of rake angle to the forks, lots of trail at the front tire. Raising the rear of the bike will cause minimal change to the front fork angle, maybe 1/2 of one degree.

Tony Foale wrote the book on motorcycle chassis geometry. He even built an adjustable front forks for a test bike, so he could reduce the fork angle to study the results. The results proved that trail has more effect on stability than rake angle, even to the point he built a test setup with zero fork angle and about five inches of trail and the bike was fully stable at all speeds.

[Mechaniac]

LOL, zero fork angle and five inches of <castor> then, like a grocery cart. Not laughing at you but just the test to prove what anyone who was pushed around the market as a toddler should have figured out.

I went through many posts, some said they couldn't tell a difference, others that it was more willing to turn in. I operate machines right at their limits at times and can tell a change. Also I've been known to set the cruise and take my hands off the bars to adjust the music on my phone sometimes for a short distance. Last thing I want is a death wobble. I'm going with the better geometry and shorter stopping distance for this heavy girl.

Vernon

[Mechaniac]

https://www.rideapart.com/news/24605...-bias-or-both/

[andyvh1959]

Interesting, thanks for posting that link. I was not aware of any stock production bikes being fitted with radial and bis-ply tires.

On my VN1600 Classic, I changed both the front and rear wheels to the 17" Mean Streak wheels and radial tires. Did not notice any changes in chassis dynamics due to the changes. And I didn't expect any changes since the Mean Streak has very similar chassis geometry to the Classic and Nomad.

[mick56]

Tyre squeal in 3rd ? Mine wont even do that in 1st. What power is it poking out, to do that ?

[Mechaniac]

Originally Posted by mick56

Tyre squeal in 3rd ? Mine wont even do that in 1st. What power is it poking out, to do that ?

The correct answer to this question is always "Not enough.". Mods are Cadman style dual open air filters. Iridium plugs. Cobra Fuel Processor road tuned. Vance and Hines Bagger exhaust pipes. Redline Lightweight Shock-proof Gear Oil in the diff (Smurf Blood). Liqui Moly synthetic oil. Lightened flywheel 19.4 lbs. to 14.6 IIRC. I flushed the fuel system with several tanks including Sea Foam when I picked it up about 2500 miles ago. Also installed a super light weight battery in reverse pole Harley size, it was a tight fit, dropped down to about 2 lbs maybe three from fifteen or whatever it was.

The fuel processor was not correctly adjust when I bought it so that, the dual air breather conversion, and the flywheel have been my biggest gains. Flywheel was the most dramatic, adjusting the fuel in right was pretty good.

I dropped my original, low miles (<10K), flywheel off with my racer friend today. Him and his crew are getting three cars ready to test and tune this weekend at Baytown Speedway and then packing up to race in Florida next month. In between he's going to duplicate the flywheel shave and balance job. So, I'll have one for sale soon. I don't know how much yet but nothing crazy. I'd like to sell it with a core exchange until he gets tired of it LOL.

Vernon

[Mechaniac]

Here's a link to Gadgets site if you don't know about it, it's the bomb. I've done many of the mods documented here.

http://www.vulcangadgets.com/files/caddmankit.html

Vernon

[blowndodge]

Why not just buy a faster bike?

[Mechaniac]

The ones I like cost about this much. I was poor most of my life, I don't like to spend big money to do what I know how to for little money. I'm just having fun, this is my main hobby. I can afford to buy the fastest things and then spend the money to make them them faster but I'm not that fun greedy, if that makes any sense.

https://www.cycletrader.com/listing/...E-S-5023014457

Vernon

[mick56]

Originally Posted by Mechaniac

The correct answer to this question is always "Not enough.". Mods are Cadman style dual open air filters. Iridium plugs. Cobra Fuel Processor road tuned. Vance and Hines Bagger exhaust pipes. Redline Lightweight Shock-proof Gear Oil in the diff (Smurf Blood). Liqui Moly synthetic oil. Lightened flywheel 19.4 lbs. to 14.6 IIRC. I flushed the fuel system with several tanks including Sea Foam when I picked it up about 2500 miles ago. Also installed a super light weight battery in reverse pole Harley size, it was a tight fit, dropped down to about 2 lbs maybe three from fifteen or whatever it was.

The fuel processor was not correctly adjust when I bought it so that, the dual air breather conversion, and the flywheel have been my biggest gains. Flywheel was the most dramatic, adjusting the fuel in right was pretty good.

I dropped my original, low miles (<10K), flywheel off with my racer friend today. Him and his crew are getting three cars ready to test and tune this weekend at Baytown Speedway and then packing up to race in Florida next month. In between he's going to duplicate the flywheel shave and balance job. So, I'll have one for sale soon. I don't know how much yet but nothing crazy. I'd like to sell it with a core exchange until he gets tired of it LOL.

Vernon

That doesn't sound anything like tyre sqeualling mods to me. But hey

[andyvh1959]

If you are looking to get tire squel in 2nd or 3rd gear be aware, for that beware, of the transmission issues the 1500/1600 are well known for. I bought my 1600 Classic in great shape, with all the Gadgets mods applied, for only $1200 because 2nd gear crapped out. I have to pull the engine and split the cases to fix what is likely a failed shifter fork. You best be very good about shifting or have built up the tranny on your Vulcan if you plan to hit it hard in the three lower gears.

[ldhthept]

The Meanie is such a fun ride and with the big three done it really opens it up. I had an 03 that I had the dual Cadman’s, Cobra fuel processor, and Hard Krome exhaust. I changed to just a single Cadman on R side, didnt see the need for both other than a balanced look. Do you get that much more air in with the dual set up and able to control it with the fuel processor? I recently bought one that sat for over 15 years completely stock, am trying to get it running correctly and then decide to keep or move on.

[Mechaniac]

Exactly, it's great looking V-Twin cruiser than can hustle, fun indeed.
I did the Cadman with dual Spectre's 9x2 mainly for the balanced look. I didn't know that the factory set up was to breath from the other side and pipe it through until I started in. It made a seat of the pants difference that was remarkable.

This bike feels a bit beyond what I expected a 1600 named mean streak should have felt like from the factory now. If my fuel processor had been properly adjusted from the get go I may have been satisfied with it enough to leave it alone and just ride. But it was a bit sluggish so I started down the fix it rabbit hole and it's not spiraled out of control but fell together quite nicely to be a super bike when done. It just hit 10K miles and is in good condition. I'll probably sport it for many years after all of this. If you ride with V-twin guys but feel the need for speed like I do it's a great bike. My Super Magna is a drag bike tour-de-force but a little small for me these days. I'll never get rid of it again but this Mean Streak is a great companion that can take us on longer rides to places where the curves are legendary.