Larger Front Tire (and raise the front Fender)

[DAN]

This post is a spin off of "Larger rear Tire" Thread also here in "How To's". You may want to look at the "Larger rear Tire" subject posts as they will have more information if you are changing both front and rear tires.

The standard Front tire on the GZ 250 is a 110/90-16. You could also use a 120/80-16 and have the same diameter. My 1999 GZ came with Dunlop D-404 tires. They are only avalable from Suzuki as "original equipment" not on the general market from Dunlop. The smallest Dunlop D-404 is a 130/90-16. This is the same size as a "Harley" front tire so I call it the GZ 250 "Fat Boy". After consulting directly with The Dunlop MC Tire customer service rep, I was sent via fax the rim size tolerance charts showing the 130/90-16 is within the allowed limits for the GZ 250 rims (both the front 130/90-16 and the larger rear 140/90-15 D-404's are approved by Dunlop for the corrisponding GZ rims). I changed both the front and the rear tires to these D-404 larger respective sizes.

Here are the points of consideration you will have to take into account if you make these tire size mods.

The GZ will be 3/4 of an inch taller and the ground clearance will also be 3/4 of an inch greater (no more dragging the left exhaust pipe over the curb). There is a side effect to this though, The kick stand foot will require a point 7 to point 75 inch foot. I bolted on a 4 inch by .7 inch aluminum extrusion (half of a telescope dovetail bar) that did the job nicely. Will post kick stand picture.

The front fender will have to be raised aprox. one inch. I only raised mine 3/4 inch (as seen in picture) and recommend at least 1 inch or more.

This thread is an explanation of how to raise the fender. To be continued next.

[DAN]

The Front fender is bolted to the forks from inside the fender. Take special note of the fact that the bolts have a "shelf" or stop ridge between the bolt cap and the threaded part. This is to make sure you do not crush the ABS plastic fender and crack it. If you add a reinforcing bracket to the inside of the fender as I did, YOU WILL HAVE TO ADD METAL WASHER/SPACERS INTO THE FENDER to keep from crushing it. The thickness of the spacers is just a little less than the fender thickness. Look at the original mounting bolt, put it into the fender and you will see the correct spacing required. You may wish to make up your own mounting system, but all I did was to put four 1/8" by 3/4" wide and about 2 inches long aluminum flat bar stock (two on each side forward and aft of the fender fork hump) on the inside of the fender as reinforcments using the same original fork fender bolts. The original hole in the fender is aprox 3/8" (i'm sure it is some metric number), this original hole is used to bolt the upper reinforcing bar hole to the fender. An additional hole is drilled through the fender EXACTLY one inch lower. Be precise in the placement of the new lower holes (4 new holes, two on each side), these holes effect the tilt forward and aft of the fender in relation to the wheel so measure them carefully. If you drill all of the support brackets the same (stack them) you should get the correct position of the fender. Drill the ABS plastice of the fender with a proper drill bit (wood bit with a wing tip - I used a 3/8th's bit and a very slight round fileing for the washers to fit) and use a wood backing block with a drill press to keep your work steady and solid. I would not reccommend "free hand" drilling as this could grab and jerk, probably cracking the Plastic of the fender. This is a fairly simple task as the fender will slide up and fit between the forks just fine.

The kick stand shoe extention was a simple drill through, taper counter sunk bolt up with one bolt being longer to go all the way through the kick stand shaft (see picture)

[DAN]

How does it ride? Well it has a 3/4" higher seat and this does seem to make the feel a little taller. The basic ride is the same, but over 40 mph you will notice a bit more stability, probably caused by greater gyroscopic forces in the wheels (greater rotating mass). The steering is completly neutral, no pull into or out of a turn. The 110's on my bike had a very slight pull into a turn and had to be steered out, the 130's just seem balanced. The speedo now seems to tell the truth instead of reading higher than the true speed with the 110's. The greater diameter on the rear tire (140/90-15) is equivelent to a 15-1/2 tooth drive sprokett. The over all look of the bike is that of a full size MC instead of the 90% scale MC with the original tire sizes. I like the GZ 250 "Fat Boy" for both ride and looks. It might not be to everyone's taste, but some may like it. --Dan--

[Water Warrior 2]

Very nicely done Dan. Having 2 bikes is even better than before and after pics.

[blaine]

Originally Posted by DAN

The speedo now seems to tell the truth instead of reading higher than the true speed with the 110's. The greater diameter on the rear tire (140/90-15) is equivelent to a 15-1/2 tooth drive sprokett. --Dan--

mrlmd1 wrote:
"This will raise the bike a whopping .354 inches."
And that's at rest, unmounted, not weighted down on the bike by the weight of the rider, fuel, frame, etc, compared to the other tire. So the effect is probably not even measurable or noticeable by a rider. If the tire diameters were actually measured on a fully loaded bike, my bet would be that they are even closer in measurement than what WW posted,
I think the difference is in your head. :poke2: :neener:




I knew it wasn't just in my head. :tongue:

[Water Warrior 2]

Weighed down or not with the rider the bike will still be raised that little bit. Taller tires mean a taller bike. And you will feel a difference in height when you climb on the bike. You can feel a difference between thin soled shoes compared to riding boots or hiking boots with a thicker sole. Same thing just from a different perspective.

[burkbuilds]

Good information and a nice write up. You did a good job with your research and I like the new look of your GZ. Well done.

[Water Warrior 2]

Dan, I was just playing with some numbers. Going by the original front tire size and the replacement your speedo should be within 1% accuracy. Check it out with a GPS for sure. The usual speedo error is 7% just to keep corporate lawyers happy and actually make you think you are just tearing up the streets.
Also my earlier tire height numbers might have been wrong. My figures now tell me the front will be 1.4 inches higher overall which will raise the bike 0.7 inches.

[DAN]

NUMBERS NUMBER NUMBERS, Well in reference to the height numbers; the rear height rise going from the 130/90-15 to the 140/90-15 is a rise of half the difference in tire diameter or in this case - 4 tenths of an inch. On the front axel the the calculated rise in going from the 110/90-16 to the 130/90-16 is an axel height increase of .75 inch. The average height rise for the GZ is just under .6 inch (.575"). Howerver there is a consideration here as to how this effects ground clearance. The left exhaust pipe drops below the frame to cross over and seems to be the lowest point of contact. The exhaust pipe is much closer to the front axel and will gain aproximately 0.7 inches of extra clearance, this being confirmed by a direct mesument. Having made this measurment while trying to steady the bike upright with one hand and eyeballing a tape measure while kneeling next to the GZ, I will state that the measurment will only be within +- 0.1 inch or so for accuracy, if that. Now the seat height increase will only be about 0.5 inches as it is closer to the rear axel.

So you gain 0.7 inches ground clearance and about 1/2 inch in seat height.

What does this mean in real life; well the biggest plus is the ground clearance as now I don't scrape the exhaust pipe when driving up over a curb. That little 0.7 inch increase made a big difference. The sitting position height rise is just noticable, but the entire bike feels bigger and when you stand back to look at it the GZ looks much bigger especially from the front quarter view, accually quite impressive from the front.

The front tire controlls the speedo and is about a 6% lower reading than the 110/90-16 which in real life makes the 130/90-16 front wheel read very close to the actual true speed of the bike.

The rear tire size increase is the equivelent of going to a mythical 15-1/2 tooth drive sprocket. --Dan--

[emory70]

i tell ya, i don't care about the numbers. what i do like is the expanded options for tires with the larger sizes.