Streetbox
The Hyperpro Streetbox includes a progressive front fork spring kit and an adjustable emulsion shock. This comprehensive solution improves cornering, braking, and overall bike balance, making it ideal for street use.
Additional Notes:
Compatible vehicles:
- 1987-1993 KAWASAKI GPZ 500 S
Pickup available at EPM Performance Imports
Usually ready for pickup or shipment in 1-2 weeks.
Streetbox
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EPM Performance Imports
Pickup available, Usually ready for pickup or shipment in 1-2 weeks.
3 Fedornak Freeway
Unit 1
Whiting NJ 08759
United States+17327869777
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Let customers speak for us
5 star
Everything I wanted and never knew I needed. Spec’d perfect. Didn’t even have to adjust sag.
100 times better than stock, wife on back says nothing compared to ouch or ugh when we hit a bump
I have spinal stenosis, this was exactly what I was looking for.
huge improvement !
replaced the ktm garbage, which had completely failed and was bouncing and bouncing and bouncing
Excellent service throughout. Thank you!
Fits perfectly
Very high quality
If you have a 40–50 lb rider on a Husqvarna EE 5 (or KTM SX-E 5 / TC 50), swapping out the factory shock spring for this 25 N/mm spring is hands-down the single best suspension upgrade you can make.
The stock rear spring is notoriously oversprung for young kids. Before installing this, our rider was getting bucked over braking bumps, the rear end skittered out in flat turns, and it was physically impossible to dial in correct rider sag—even backed all the way out on the preload collar.
Swapping to the 25 N spring completely transformed the bike's balance:
True Sag Numbers: Finally allowed us to set proper race sag (targeting ~60–65 mm) while still maintaining healthy static free sag.
Chassis Balance: Balances out the front WP air fork so the bike stays level and planted instead of riding stinkbug into turns.
Instant Confidence: The rear wheel actually tracks through acceleration chop and ruts now rather than deflecting. Our rider felt the difference on lap one—much less fatigue and far more control over rough, choppy sections.
Fit and finish (47x130) are spot-on, drop-in replacement with the stock WP shock collars, and the coating holds up to roost and power washing. Don’t waste time fighting the stock spring if your kid is under 55 lbs—this 25 N spring fixes the rear end completely. Highly recommend!
Awesome addition to the 390. The spring had made 2 up riding much more comfortable.
Sterrring damper is amazing! Got rid of all the head shake at high speeds. I only have it 5 clicks in and it's working as it should. The guys at EPM are great. Thanks!
Got shipped out right away
Easy to install
Was experiencing crazy tank slappers on my mt09 I bought this to try it out,absolutely game changing I have not experienced any sort of wobble since!
arrived quickly and packaged perfectly. Thanks.
